The increasing crowding of the electromagnetic spectrum as well as increased power demands of mobile devices both spur interest in wireless energy harvesting.
Typical energy harvesting devices are comprised of an antenna which induces AC current from gathered ambient EM radiation, and an AC-DC converter which converts the AC current to usable DC current. Simple energy harvesting devices have a simple rectifier and an antenna; combined, the devices are called rectennas (rectifier-antenna).
While dealing with low voltage values that are induced from a typical dipole antenna, a simple diode, is often sufficient for a safely operational harvesting device. Nevertheless, where a significantly more potent antenna such as a split phase flattened-torus antenna is used, there is a need for more complex rectifiers that as unneeded by-product often have larger dimensions due to increased usage of durable components.
It is obvious to one of average skill in the art that while a simple diode rectifier is enough when dealing with perhaps tens of millivolts and several milliamps of voltage a simple antenna, the same device, may not possibly endure a split phase flattened-torus antenna or other potent antennas with tens of volts and a hundred or more milliamps of voltage output.
Designing a compact transducer comprised of relatively few and light components for converting tens of volts AC to the 5V DC voltage and one-hundred or more milliamps that is suitable for charging mobile devices such as phones and tablets, is not an easy task.
A person of average skill in the art will face several difficulties while trying to achieve such a design.
Due to the split phase antenna used in conjunction with the transducer, and due to the relatively high voltage derived thereof, advisable is a parallel rectifier configuration to reduce the load on each rectifier.
In addition, due to the pulse nature of antenna derived current, there is a need for a capacitor to smooth the current for suiting sensitive mobile devices. The addition of a capacitor is problematic because suddenly disconnecting a capacitor from the source in order to connect it to the load may result in a massive spike in voltage (flyback) which may cause the device to explode or otherwise damage components.
Furthermore, where the device dimensions are limited, such high power as is expected from potent antennas, is catastrophic to the device components (diodes and capacitors). There is a need for a device that has a combination of components which enables the following characteristics:
A) compact device dimensions;
B) endurance of high AC power input from a split phase source;
C) the flyback effect resulted from the split phase configuration is prevented;
D) smooth DC voltage output suitable for mobile devices, typically 5V at 100 or more milliamps DC;